Getting ready to do my first ever 7 day fast tomorrow looking for advice...

Just curious if It's ok for me to drink stuff like black tea and black coffee and still get the autophagy benefits? I got some of the unflavoured LMNT electrolytes to take daily as I plan to continue my usual workout routine and cardio exercise while doing this. I also saw in the sidebar that a fasting state lowers your immune system will this make me more susceptible to getting sick? What should i eat on my first day back to normal eating? Any help is much appreciated thanks.